Loans - Amounts of Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Jun. 30, 2020	Jan. 01, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan Balance	$ 4,030,365			$ 3,634,596
Allowance for loan losses	(56,319)	$ (55,090)	$ (22,577)	(17,667)	$ (17,956)	$ (18,305)	$ (17,820)
Outstanding Balance				3,636,841
Loans, net	3,974,046			3,619,174
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable				2,046,651
Loan Balance	2,321,608			2,047,646
Allowance for loan losses	(39,795)	(39,147)		(11,996)	(12,082)	(11,881)	(10,495)
Real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Real Estate, Total				770,717
Loan Balance	1,049,873			920,998
Allowance for loan losses	(5,464)	(5,832)		(923)	(1,449)	(1,732)	(1,676)
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable				669,180
Loan Balance	658,884			665,952
Allowance for loan losses	(9,810)	(8,921)		(3,671)	(3,384)	(3,652)	(4,643)
Working capital and equipment | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable				938,317
Real estate, including agriculture | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable				978,891
Tax exempt | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable				63,571
Other | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable				65,872
1–4 family | Real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Real Estate, Total				762,571
Other | Real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Real Estate, Total				8,146
Auto | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable				362,729
Recreation | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable				16,262
Real estate/home improvement | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable				43,585
Home equity | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable				237,979
Loan Balance	260,536			276,215
Unsecured | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable				7,286
Other | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable				1,339
Mortgage warehouse
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan Balance				150,293
Allowance for loan losses	$ (1,250)	$ (1,190)	$ 0	$ (1,077)	$ (1,041)	$ (1,040)	$ (1,006)